Verifications of Resistance to Phytophthora spp. in 2-year-old Citrus junos Cultivars and Related Species

Abstract

Yuzu (Citrus junos) gummosis disease, caused by Phytophthora nicotianae, was first reported in 1997. Asknown in citrus, Phytophthora is the most fastidious soil-borne pathogen to control. In order to minimize itsdamage to Citrus spp., integrated pest management (IPM) approach, including fungicide chemicals andresistant cultivars, is necessary. Therefore, in this study we tried to evaluate tolerance of yuzu cultivars and itsrelated species against yuzu Phytophthora. Trifoliate orange was evaluated as a susceptible host to yuzuPhytophthora by both mycelial growth onto extract media and immature fruit inoculation. However, inzoospores spray-inoculation on 2-year-old cuttings tree, trifoliate orange appeared to have a resistant propertyas showing less than 6% diseased leaf rate. Among yuzu cultivars only ‘Namhae No. 1’ appeared resistantproperty against both P. nicotianae and P. citrophthora. The ‘Namhae No. 1’ showed 5.7% and 10.6% diseasedleaf ratio by P. nicotianae and P. citrophthora, respectively. Clearly, in order to reduce damagescaused by two yuzu Phytophthora, we suggest that growers may utilize a trifoliate orange as a rootstock and‘Namhae No. 1’ as a scion for fruit production.